Reduction of Np(VI) in Irradiated Solutions of Nitric Acid

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The reliable separation of neptunium from dissolved nuclear fuel assumes the ability to maintain a preferred oxidation state. However, regardless of its initial redox speciation, a series of reactions occurs in nitric acid to create a mixture of oxidation states including Np(V), Np(VI) and sometimes Np(IV). To further complicate the situation, irradiated solutions such as fuel dissolution contain both transient and long-lived radiolysis products which may be strongly oxidizing or reducing. Thus, irradiation may be expected to impact the equilibrium distributions of the various neptunium valences. Among the transient products of the irradiation of aqueous nitric acid are the reducing ... continued below

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Precek, Martin; Paulenova, Alena & Mincher, Bruce J. September 1, 2012.

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The reliable separation of neptunium from dissolved nuclear fuel assumes the ability to maintain a preferred oxidation state. However, regardless of its initial redox speciation, a series of reactions occurs in nitric acid to create a mixture of oxidation states including Np(V), Np(VI) and sometimes Np(IV). To further complicate the situation, irradiated solutions such as fuel dissolution contain both transient and long-lived radiolysis products which may be strongly oxidizing or reducing. Thus, irradiation may be expected to impact the equilibrium distributions of the various neptunium valences. Among the transient products of the irradiation of aqueous nitric acid are the reducing •H atom and solvated electron (e-aq) and the oxidizing •OH radical from water radiolysis, and the oxidizing •NO3 and •NO2 radicals from nitric acid radiolysis. Longer-lived radiolysis products include hydrogen peroxide from water radiolysis and nitrous acid from nitric acid radiolysis. It has long been known that HNO2 acts as a reducing agent toward Np(VI); however, the effects of the oxidizing transient species have been less well studied. Here we have irradiated nitric acid solutions of neptunium with 60Co gamma-rays, and measured radiolytically-induced changes in neptunium valences, as well as the nitrous acid concentration, by UV/Vis spectroscopy. It was found that in 4M HNO3 at low absorbed doses, the oxidizing radicals oxidized Np(V) to Np(VI). However, as the irradiation proceeded the concentration of nitrous acid became sufficient to reduce Np(VI) to Np(V), and then continued irradiation favored this reduction until an equilibrium was achieved in balance with the oxidation of Np(V) by nitric acid itself. The starting abundances of the two neptunium valences did not affect the final equilibrium concentrations of Np(V) and Np(VI), and no Np(IV) was detected.

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  • Atalante 2012,Mount Pelier, France,09/02/2012,09/07/2012

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  • Report No.: INL/CON-12-26355
  • Grant Number: DE-AC07-05ID14517
  • Office of Scientific & Technical Information Report Number: 1060971
  • Archival Resource Key: ark:/67531/metadc842446

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  • September 1, 2012

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  • May 19, 2016, 9:45 a.m.

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  • Dec. 1, 2016, 1:46 p.m.

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Precek, Martin; Paulenova, Alena & Mincher, Bruce J. Reduction of Np(VI) in Irradiated Solutions of Nitric Acid, article, September 1, 2012; Idaho Falls, Idaho. (digital.library.unt.edu/ark:/67531/metadc842446/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.